Cystatin C concentration is correlated with disease activity in rheumatoid arthritis patients

Rheumatoid arthritis (RA) is a systemic, inflammatory disease. Renal involvement worsens the course of RA and increases mortality. It is suggested that chronic inflammatory processes may contribute to renal impairment. The aim of this study was to investigate the impact of chronic inflammation and RA activity on glomerular filtration rate (GFR).

The study population consisted of 140 RA patients. High disease activity was observed in 42 patients (30%), and long-term RA (duration ≥ 10 years) in 64 (45.7%). Measures of renal function included: serum cystatin C, serum creatinine (SCr), and creatinine-based estimated GFR (eGFR) calculated by Cockcroft and Gault (CG) and Modification of Diet in Renal Disease (MDRD) formulas.

The mean (SD) cystatin C concentration was 0.77 (0.2) mg/L, SCr 0.71 (0.23) mg/dL, eGFR(CG) 110.5 (37.8) mL/min/1.73 m², and eGFR(MDRD) 109.5 (34.5) mL/min/1.73 m². Cystatin C levels correlated positively with creatinine, and negatively with eGFR(CG) and eGFR(MDRD). Cystatin C concentration was significantly higher in patients with high disease activity, long-term RA, and hypertension, and in males. Patients currently being treated with biologics had non-significantly lower cystatin C levels than those treated with conventional modifying drugs. Cystatin C levels were significantly associated with markers of clinical, functional disease activity, and markers of inflammation. By contrast, there were no such correlations with other parameters of renal function.

In patients with RA, cystatin C may be not only an indicator of GFR but also a marker of intensity of chronic inflammatory processes.